Motion picture sound recording and reproducing system



June 22, 1943. l. R. GOSHAW MOTION PICTURE SOUND RECORDING ANDREPRODUCING SYSTEM Filed Aug. 2, 1941 2 Sheets-Sheet l IE1. R @osHA WAna/F152 OSCILLA 10,2

OSCILLAYI y R W m e m w v T m A of modulated tracks for variouspurposes.

Patented June 22, 1943 UNITED STATES PATENT OF Fi-CE MOTION PICTURESOUND RECORDING AND REPRODUCIN G SYSTEM Irl R. Goshaw, Beverly Hills,Calif., assignor to Radio Corporation of America, a corporation ofDelaware Application August 2, 1941, 'Serial No. 405,239

15 Claims.

in this area or areas for controlling the speed of a motor, while U. S.Patent 2,199,599, dated May 7, 1940, to Dawson, discloses a signalamplitude control track in this area. Copending application Serial No.181,634, filed December 24, 1937, shows a type of control track systemsimilar to Dawson's.

In each of these disclosures, however, the discontinuity of the soundtrack caused by the sprocket holes has been taken into consideration.For instance, in Patent 1,921,494 only the intermittent or absolutevalue of the light passin the photoelectric cell during the stationaryperiods of the film is utilized to operate a solenoid in a mechanicalcontrol system. This is perhaps the simplest form of utilization of thesprocket hole areas since the amount of light passing to the cell duringthe stopping time of the film controls the armature of the solenoid. Itis obvious' that such a system will not produce a smoothly varyingcontrol current.

In Patent 2,199,599 and the above-mentioned copending application thesprocket holes have been utilized to produce a carrier frequency whichis modulated by the varying opaqueness of the areas between the sprocketholes, it being necessary, of course, to pass the modulated carrierthrough a detector or rectifier before impression upon. an amplitudecontrol element such as a variable gain amplifier in the signal currenttransmission channel. Such a system requires smoothing filters afterdetection or rectification. as is well known in the art. Furthermore,Patent 2,199,599 has emphasized the necessity of a filter networkbetween the pickup photoelectric cell and the detector for reducing thewave to an approximately sinusoidal form. Similarly, intheabove-mentioned copending application the modulated carrier current ismodified by the use of either selective circuits or a transformer-tunedto the sprocket hole frequency, the selective circuits and transformerbeing connected between the photoelectric cell and a detector orpreamplifier. Furthermore, such systems are limited in the rapidity oftheir control action to less than 96 cycles per second, the sprockethole frequency.

The present invention, however, utilizes this sprocket hole region ofthe film but with the regular sound recording and reproducing elementswithout the additional filters, networks, detectors or rectifiersmentioned above. In other words, thi sprocket hole area may be, recordedupon and reproduced in exactly the same manner as any solid or uniformsound track area not having discontinuities. Thus, a signal or controlcurrent as exactly recorded can be reproduced with a simple amplifyingsystem without the above-mentioned additional elements.

This is accomplished by rotating the recording and reproducing slits atan angle which at all times impresses light on the same amount ofrecordable film area duringrecording, and upon the same amount ofrecorded film area during reproduction. That is,ithe invention may beused for film having othertypes of regular discontinuities such as aseries of opaque areas, as well as-sprocket holes, it being necessary inevery case that the slit see the same amount of recordable or recordedfilm at any instant. Thus, in the standard type of 35 mm. sound film,the slit will be positioned at an angle of approximately to its normalposition 01' 30 to the direction of movement of the film, since thedistance between similar points on the sprocket hole area longitudinallyof the film is in the neighborhood of .187 inch, and the width of thesprocket hole is .110 inch, the tangent of this angle thereby beingsubstantially 595. When 'while Patcnts 1,917,653 and 1,928,953 showrotated slits for recording normal sound track areas and claim certainadvantages therefor. None of these disclosures, however, discloses theutilization of the sprocket hole region of the film as evidenced by theslit angles suggested therein. The principal object of'the invention,therefore, is to facilitate the recording of signals on motion picturefilm.

' Another object of the invention isto increase the utilization of amotionpicture film for signal recording.

v A further object of flieinvention is to utilize for signal recording afilm region having a series of nonrecordable areas therein.

A further object of the invention is to utilize the areas between thesprocket holes of motion picture film without the use of any additionalap aratus other than that required for normal sound recording andreproduction.

A further object of the invention is to utilize the areas between thesprocket holes of motion picture film for one or more control records.

Although the novel features which are believed to be characteristic ofthis invention will be pointed out with particularity in the appendedclaims, the manner of its organization and the mode of its operaflonwill be better understood by referring to the following description readin conjunction with the accompanying drawings forming a part thereof, inwhich Fig. 1 shows a soimd track of the variable density type recordedin the areas between the sprocket holes of a motion picture film;

Fig.2isa =1 cofasoundrecording system for recording sound in the areasbetween the sprocket also showing how the system may be utilized forcontrol track recording;

' light reaching the photocell is modulated by the r same amoimt of filmat any instant.

Referring now to Fig. 2, a normal recording system is illustratedwherein light from a lamp I2 is collectedv by a lens l3, projectedthrough aperture ll of a mask it past a,penumbra shutter II and througha lens II to amirror II of a galvanometer it. The light is reflectedfrom the signal picked up by a microphone 28 and im- Fig. 3 isa c viewof a recording system for a multiplicity of control signals;

Fig. 4 is a ditic arrangement of a reproducing system for a signalrecord and also showing how the sprocket hole record may be used forcontrolling the signal record; and

' r Fig.5 is a reproducing system for the recording system of Fig. 3.

Referring now to Fig. 1, this figure is a partial view of the sprockethole and sound track regions of a sound and motion picture film 5showing the sprocket holes 8 and the portions or lands 1 between thesprocket holes upon which a variable 1 density control track has beenrecorded. The regular signal record is shown at 8. To ilius-- tional to.the ratio of the film area between the sprocket holes-to the sprockethole area. Aside from this reduction, this portion of the film may betreated as any solid film portion, the sprocket holesbeing ignored asfar as recording and reproduction are concerned.

To further illustrate, the slit shown at ll extends across one hole andone land. when the film moves along .to a point shown by the dotted slitll, itwill be observed that the same amounts of hole and land are acrossthe slit but reversed.

pressed on the galvanometer I! through an amplifier 29. Such a recordingsystem will provide a variable density sound track as shown in Fig. 1when the slit ll, galvanometer mirror II, and silt ll are tilted to anangle of approximately to the direction of motion of the film 2i.cording in accordance with the invention may also be accomplished byleaving the optical recording element in their regular position fornormal sound recording and rotating the direction oi film motionsubstantially 60. Furthermore, other types of light modulators andvariable density recording systems may be used, such as lightvalves,glow tubes and the like.

If it is desired to record on this sprocket hole area a comparativelylow frequency control track for various purposes such as the amplitudeconin location along the slit. As the film is advanced "area at oppositeends of the slit. in positions It and It.

Thus, the recordable film area shifts back and forth across the slit butis always of the same length or value regardless of its position alongthe slit. In reproduction, thereior the trol of a signal record, it isonly necessary to connect the galvanometer I! to a source of potential.30 which may be varied in its impression on the galvanometer by arheostat II as shown by the dotted lines. The potential may be manuallyvaried or automatically varied in accordance with the type of systememployed. An-oscillator whose frequency is varied in accordance with theamount of control desired may also be used.

Referring now to Fig. 4,'there is shown a reproducing system for thesimultaneous reproduction of the regular sound track and the sound trackin the sprocket hole area. This system utilizes a lamp 3!, a lens 34, aslit mask ll, and

a lens 36 which projects a narrow beam of light transversely through thesound track area to a photoelectric cell 31 in a'manner well known inthe art. The cell output is amplified by a standardamplifier 39 and mayor may not be impressed upon a variable gain amplifier III beforeimpression on a loudspeaker 2. This is the normal sound reproducingsystem well known in the art wherein the variable gain amplifier ll maybe varied in amplification to control the output amplitude of the soundat 42.

For reproducing the signal track in the sprocket hole area, a similaroptical system ineluding a lamp 5, a lens 46, a slit mask 41. and a lens48 is utilized to project light through the sprocket hole region to aphotocell 50. It is to be noted, however, that wherein the slit II'scanning the regular sound track area is positioned transversely of thefilm, the slit l2 scanning the snrockethole region is at an angle, asdescribed 'in Fig. l, which is the same as the angle of the slit 23 inFig. 2. The output of the cell [0 is impressed upon an amplifier El andthen to a loudspeaker 52. It is realized that a variable gain be theexact duplicate oi the regular signal channel portion of the systemexcept for the angle of the slit 52. If the sprocket hole film regionhas been recorded as a control record for the ampli-' tude of theregular sound track signal by manipulation of the rheostat 3| in Fig. 2,it is only necthe control record are limited to control currentvariations below the frequency of the carrier current and also limitedto the number of control currents which may be recorded and reproduced.

The present system is not so limited.

In Fig. 3, a multiple signal film recording system is illustratedwherein the same recording optical elements of Fig. 2 are shown. Sincethe sprocket hole area'now operates in the same manner as the solid filmarea,any type of track may be recorded on this portion of the film.Thus, it is possible to record a plurality of carrier frequencies onthis area, each carrier being individually modulated for controlling aplurality of functions or characteristics of a signal. This isaccomplished by the use of carrier frequency oscillators shown at 55, 55and 51, each of which has a different frequency. The output of eachoscillator may be modulated as diagrammatically shown at 58, 59 and 60,respectively. The modulation may be either by amplitude or frequency, asillustrated by the variable resistances (amplitude modulation) andvariable condensers (frequency modulations), the output of eachmodulator being impressed upon the galvanometer la, the track thusrecorded containing each modulated carrier frequency.

Referring now to Fig. in which the reproducing system for the recorderof Fig. 3 is illustrated, the same optical systems as shown in Fig. 4may impression upon respective loudspeakers 64 and 85. Although thistype of signal system is illustrated, it is to be understood that othercombinations of controls for the signal output may be employed such asone wherein the control signals simply operate relays for connecting oneor more speakers to the output of the variable gain amplifier 40.

Referring now to the control track system, the

output of the amplifier 5| is impressed upon a plurality of filters58,59 and which are bandpass filters tuned to their respective oscillatorfrequencies and of. a band width sufiicient to take care of themodulation side bands. The output 01' each filter is impressed upon itsrespective detector and filter units I2, 13 and 14, these units fier 52for individually controlling the amplitude of the signal currentreproduced at loudspeaker 54. This reproducing system therefore providesa multiple system of control wherein the loudspeaker 84 may representthe center speaker or speakers in a theatre, and the loudspeaker 65 mayrepresent the speakers located at the sides of the stage or along thesides of the listening area toenhance the reproduced sound. Bymanipulation of the modulator unit 58, .the volume of all speakers maybe raised or lowered, while manipulation of modulator 59 may control thecenter speaker, and manipulation of the modulator 60 may control theside speaker separately from the center speaker.

The above-described recording method and system thus permits not onlythe recording of normal signals in the areas between the sprocket holesof a motion picture film, but'permits these areas to be used to recordcontrol signals without the use of filter networks. It is realized,however, that in case of mutilated film, random 96- cycleimpulses may begenerated and although this would be immaterial in a carrier frequencycontrol track system as shown in Fig. 5, it might be desirable to inserta 96-cycle elimination filter in an amplitude modulated system such asshown in Fig. 2, although it is not necessary as the amplitude of theseimpulses would be comparatively low whenever they occur. modulation ofthe control current mutilated sprocket holes will cause no deleteriouseffects.

be employed for scanning the signal and control It will be observed thata variable density track has been illustrated in the above system, butvar- 5 iable area tracks may also be recorded and reproduced with, theslit tilted at the same angle, it being desirable in this event toincrease the slit width so as to have its dimension lon itudinally ofthe film comparable to the sprocket hole height and the modulatingshutters operating transversely of the slit.

What I claim as my invention is: I

1. A sound recording system for recording signal on a film having aseries of discontinuities interposed along a recordable film areacomprising means for producing a light beam, means for modulating saidbeam with a signal to be recorded, and means for impressing the sameamount of recordable film area with light re-' gardless of the positionof said discontinuitieswith respect to said light beam. v

2. A sound recording system in accordance with claim 1 in which saidlast-mentioned means includes a slit mask having a slit thereinpositioned at such an angle with respect to the direction of motion ofsaid film pastsaid slit that the same amount of said recordable filmarea is including the required smoothing filters well I known in theart. The combination control system illustrated in Fig. 5 utilizes theoutput of detector 12 for controlling the gain of variable gainamplifier 40 over conductors 16, this control current simultaneouslyvarying the gain in both loudspeakers 54 and 55. The output of detectorfilter unit 13 is impressed upon a variable gain amplifier 63 overconductors "and individually controls the amplitude 01' loudspeaker- 85.The output of detectorfand filter unit 14 is impressed over conductors18 upon the variable gain amplibeing light-impressed at any instant.

3. The'method of sound recording on a film area having a series ofdiscontinuities distributed along a recordable film area comprisingmodulating alight beam and impressing the same amount of recordable filmarea with said light beam.

4. The method of recording a continuous signal record on a series ofrecordable film areas separated by non-recordable areas comprisingmodulating a light beam in accordance with the signal to be recorded andlight-impressing the same amount of saidrecordable areas at all times bysaid light beam.

5. The method of utilizing the areas of a film lying between thesprocket holes for the recording of a signal comprising forming lightinto a narrow beam, modulating said beam with said signal and impressingsaid beam on said areas be- With frequency 4tw'eenssidsprocketholesatanangletothedirectionotmotionofsaidareassothatsaidbeam.

at each instant recording.

11. The method of utilizing a film area having a plurality ofdiscontinuities distributed along a recordable film area comprisingcontinuously lightim constant amounts of said film area and saiddiscontinuities at any instant during said light impression. I

'1. a film sprocket hole area recording systeminaccordancewithclaimfiinwhichsaidheam angle is approximately to thedirection of motion of standard mm. motion picture film.

8. A sound reproducing system for reproduce ing a signal recorded on thefilm areas interposed between the sprocket holes comprising a source oilight, means for forming said light into a beam, means for translatingsaid light into electrical currents, means connected to said translatingmeans for amplifying said currents, means connected to said amplifyingmeans for translating said currents into sound waves, and means forinterposing the same amount of film area between said light beam andsaid light-to-current translater during passage of said film throughsaid sys- 9. A sormd reproducing system in accordance with claim 8 inwhich said last means includes optical means for impressing said lightbeam at an angle of substantially 30 to the direction of v movement oi.said film.

10. The method of reproducing a signal re-. corded ln.the areas betweenthe sprocket holes of a motion picture film comprising forming lightinto an elongated beam and impressing said light beam at an angle to thedirection of motion of said film so that said beam impresses the sameammmt oi film area during passage of said film past said beam.

12. A multiple signal recording system for recording in the sprockethole area of a film comprising a plurality of sources of signals ofdifierent' frequencies, means for individually modulating the signalsfrom each of said sources, means for simultaneously varying a light beamin accordance with said signals, and means for impressing said beam onthe sprocket hole areas of said film so that said beam impresses aconstant amount of recordable film area.

13. A multiple signal recording system in accordance with claim 12 inwhich said film has recorded thereon a sound track, said signals bein gadapted to control the reproduced sound from said soimd track.

14. A system for translating signal records of difi'erent frequenciesrecorded in the sprocket hole area of a film into electrical currentscomprising means for scanning said sprocket hole area with a beam oflight, means for translating said light into electrical currents, meansfor dividing said multiple signals into separate electrical circuits inaccordance with the frequencies of said signals, and means forinterposing the same amount oi film area between said light beam andsaid translation means during passage of said film past said light beam.

15. A system in accordance with claim 14, in which means are providedfor reproducing a sound track on said film simultaneously with thetranslation of said signal records into electrical currents, and furthermeans are provided for controlling the reproduction of said sound trackby said electrical currents.

IRL R. GOSHAW.

